With the advent of new high tech materials, such as high temperature/high strength ceramics, the efficient joining of these materials is a major technical issue and very important to wide use of these materials. Many of these materials cannot be produced in large component sizes. Consequently, use of such materials in large scale devices requires joining of smaller components into assemblies of the required size.
Also it is difficult, if not impossible, to make high performance ceramic materials in complex shapes. The joining of simpler shapes on the other hand allows the preparation of more complicated shaped high performance ceramic parts, provided that the joints and surrounding regions exhibit, at all required operating conditions, the same strength and durability as the basic ceramic material.
Another difficulty with large scale ceramic assemblies or components can be their relative fragility compared to other metal or polymeric structures. Shipping of such large assemblies from the site of manufacture to the site of use may well result in damage to the assembly and large replacement cost. One remedy for these problems is a robust capability for joining high temperature ceramics. This capability should include techniques for joining subassemblies in a production facility, but should also be capable of being used in a field setting, at the site of use.
One example of such a requirement is the production of large silicon carbide (SiC) heat exchanger assemblies for hot gas recuperation. This requires assembly of various tube segments, couplers, manifolds and other SiC and metal components into the large heat exchanger assembly. The joints must have sufficient strength to withstand the process pressures and handling during installation, and must also be gas tight. Another example is an accelerator application where there is a need to assemble a series of hot-pressed, high purity alumina tube segments, each about 3–4 cm in length, into a meter long dielectric-loaded accelerator assembly. In this case the joints need to have similar dielectric properties as the alumina, including very low loss and high breakdown voltage, and a pore free structure.
Another application is for joining ceramics plates to create complex structures such as conformal ceramic armor. If a low cost and efficient way to join ceramic plates such that the joint area shares similar physical and chemical characteristics with the base materials was available, complex, light weight multi-component assemblies could be assembled to conform to structures such as seats, engines, gearboxes or etc.
Hence, there exists a need to be able to join high performance ceramics, where the joint area shares the same or similar physical and chemical characteristics with the base materials.